Comparison of dimethyl sulfoxide treated highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) electrodes for use in indium tin oxide-free organic electronic photovoltaic devices

N.K Unsworth,I Hancox,C Argent Dearden,P Sullivan,M Walker,R.S Lilley,J Sharp,T.S Jones

doi:10.1016/j.orgel.2014.07.015

N.K Unsworth, I Hancox + Show 6 more

Open Access

https://doi.org/10.1016/j.orgel.2014.07.015

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Journal: Organic Electronics	Publication Date: Jul 24, 2014
Citations: 42	License type: cc-by

Affiliation: University of Warwick

Abstract

Indium tin oxide (ITO)-free organic photovoltaic (OPV) devices were fabricated using highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the transparent conductive electrode (TCE). The intrinsic conductivity of the PEDOT:PSS films was improved by two different dimethyl sulfoxide (DMSO) treatments – (i) DMSO was added directly to the PEDOT:PSS solution (PEDOT:PSSADD) and (ii) a pre-formed PEDOT:PSS film was immersed in DMSO (PEDOT:PSSIMM). X-ray photoelectron spectroscopy (XPS) and conductive atomic force microscopy (CAFM) studies showed a large amount of PSS was removed from the PEDOT:PSSIMM electrode surface. OPV devices based on a poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) bulk hetrojunction showed that the PEDOT:PSSIMM electrode out-performed the PEDOT:PSSADD electrode, primarily due to an increase in short circuit current density from 6.62mAcm−2 to 7.15mAcm−2. The results highlight the importance of optimising the treatment of PEDOT:PSS electrodes and demonstrate their potential as an alternative TCE for rapid processing and low-cost OPV and other organic electronic devices.

Highlights

Organic photovoltaic (OPV) devices are attracting increasing interest as a cheap alternative renewable energy source
We demonstrate conductive atomic force microscopy (CAFM) as a powerful tool for investigating the distribution of PEDOT:PSS solution (PEDOT) and PSS on the electrode surface, and this is combined with X-ray photoelectron spectroscopy (XPS), ultraviolet–visible spectroscopy (UV–Vis), kelvin probe and contact angle measurements to allow further insight into the effect dimethyl sulfoxide (DMSO) has on the PEDOT:PSS electrode
We have shown that the conductivity of PEDOT:PSS films can be further enhanced by treatment with the polar organic solvent DMSO

Summary

Introduction

Organic photovoltaic (OPV) devices are attracting increasing interest as a cheap alternative renewable energy source. A study by Azzopardi et al attributed 38–51% of the total cost of an OPV device to the ITO electrode [4] This high cost, along with limited energetic compatibility with frequently used photoactive organic materials, poor flexibility and tendency to crack and/or delaminate, has resulted in a strong interest to find an alternative material for use as the TCE without these disadvantages. While the use of polar organic solvents with PEDOT:PSS, either by addition to the initial dispersion or via a post-film treatment, have been shown to result in conductive films that are suitable for use in OPV devices, few studies have directly compared the two preparation methods. This promising device performance for DMSO treated PEDOT:PSS electrodes combined with their lower cost indicate the possibility of using PEDOT:PSS as an alternative TCE in low cost roll-to-roll processed OPV devices

Preparation and characterisation of the PEDOT:PSS electrodes

Fabrication and characterisation of OPV devices

Results and discussion

Conclusions